Rail transportation is generally recognized as being more economical than truck transportation for bulk commodities such as aggregates. Large quantities of such commodities can be moved by a small crew at low cost. However, rail transportation frequently loses out in competitive situations because of the cost of unloading, stockpiling, and delivering the commodity to the ultimate destination.
Even though large quantities of bulk material can be transported at low cost from one terminal to another, the burden is placed on the unloading facility to maintain the economics of this method of transportation for the purchaser of the commodity. Even if the unloading is slow, and the train is therefore delayed for a substantial period of time for the unloading to be accomplished, there is an added investment cost per ton handled for the use of the railroad equipment. One problem, in this regard, is that rail transportation is a twenty-four hour operation while many of the industries it serves operate only during daylight hours. Often a train makes good speed from origin to destination, only to be delayed several hours waiting to be unloaded. Each hour of delay adds to the transportation cost as much as an additional twenty-five to thirty miles of haul.
As an example of the efficiency of rail transport for bulk commodities, a train with a two-man crew pulling 1600 net tons at fifty-five miles per hours would be producing thirty-two times as many ton-miles per hour as a dump truck drive hauling twenty-five tons at fifty-five miles per hour.
Another problem affecting the efficiency of rail transportation for bulk commodities is that, under current methods, the quick unloading of a commodity train requires high capacity equipment and facilities which are idle most of the time. Such high-capacity equipment and facilities are expensive and add significantly to the investment cost per ton handled.
It is important for rail transportation of bulk commodities to offer ease of unloading and ease of transportation. This is particularly the case where aggregates and bulk material having a particle size ratio of over six are involved. (A particle size ratio of six means that the largest particles are no more than six times the size of the smallest particles.) Also, the amount of load that can be carried by the rail transportation system is a function of the center of gravity of the load. If the center of gravity of the load is too high, then less material can be carried. A high center of gravity will enhance the risk of derailing and/or toppling of hopper cars. Additionally, hopper cars that have relatively shallow walls and relatively small discharge openings will create difficulties when the material is desired to be discharged. With certain types of materials, the shallow walls will cause a "bridging" effect with the material within the hopper car. Thus, it becomes difficult to unload the hopper car when the hopper car reaches the destination site.
The following are some of the methods which are currently used for the unloading of bulk materials from trains.
Bottom dumping hopper cars are equipped with automatic doors that are opened automatically as the cars move over a pit, where the pit facility includes a feeder and a conveyor. Either a pit or an elevated trestle is required for this method, so that this method is ruled out at many locations. Obviously, the providing of a pit or trestle facility with associated conveyor systems is expensive.
Another method involves the use of rotary car dumpers; and these are commonly used for unloading coal at electric generating plants. Again, the equipment for unloading the cars is highly specialized and expensive.
Side dumping cars have been used for many years, but cannot be dumped on level ground. They require an elevated track on a built-up embankment for example that t he dumped material will flow over the side of the embankment and not flow back over the track.
Finally, backhoes or other unloading equipment are used to unload standard gondola cars. These methods are generally slow, promoting the delay problems mentioned above.
West German Patent Specification No. 24 51 518 describes a railway goods train with an automatic material unloader. This material unloader includes a conveyor belt located within the hopper cars to assist in the discharge of material. This system includes a conveyor belt that is located so as to create a high center of gravity for the hopper car. In particular, the conveyor belt has a return run mounted above the car platform that has troughing idlers mounted in a conventional fashion and spaced significantly from the return idlers. Additionally, this German Specification shows a hopper car having relatively shallow walls and small discharge openings. This is suitable for the transportation of sand or bulk materials having a particle size ratio of six or less. However, such a configuration of hopper car is not appropriate for the transportation of aggregates or material having large particle size ratios.
To take maximum advantage of the efficiencies of rail transportation for aggregate materials, a special type of train is needed to deliver bulk commodities on any track, at any time of the day or night, with no labor required other than the train crew. Such a train would make optimum use of labor while providing incentive wages for the crew, and thereby reduce overall labor costs.
A self-unloading train which overcomes many of the above-discussed disadvantages of rail transportation for aggregate materials may be a "unit train" consisting of a plurality of hopper cars and a trailer car, the unit train to be pulled by a conventional locomotive. Each of the hopper cars may include several hoppers having bottom discharge openings and associated gates for discharging onto an endless belt conveyor which runs the entire length of the train. These hopper cars would have walls that were inclined at relatively steep angles and have relatively large bottom discharge openings. The trailer car would include a transfer conveyor which receives the material from the train conveyor, and is movable on the trailer car to transfer the material to a selected point relative to the train.
With the unit train moving along a straight section of track, the material may be deposited in a window along the track by the transfer conveyor. Alternatively, the unit train may be unloaded while stationary, with the transfer conveyor discharging onto a portable stacking conveyor, for example, which will enable the deposit of the material in piles thirty feet high, at least forty feet away from the track, for example.
A significant development in the furtherance of this "unit train" concept occurred with the invention of U.S. Pat. No. 4,925,356, issuing on May 15, 1990 to the present inventor and to William B. Snead. U.S. Pat. No. 4,925,356 disclosed a self-unloading train for the transfer of bulk commodities that comprises a plurality of hopper cars, a train conveyor, and a gating system. The plurality of hopper cars are coupled together to form a train. Each hopper car has at least one hopper having walls inclined at shallow angles to the vertical and a bottom discharge opening having a width at least fifty percent of the distance between the wheels of the hopper cars. The train conveyor is an endless belt supported on the cars and underlying each of the hopper discharge openings. This endless belt receives the material discharge from the hopper discharge opening. The train conveyor extends for the length of the plurality of hopper cars. The train conveyor has a width that is substantially greater than the width of the discharge openings. The gating systems are operable selectively so as to discharge material from the hoppers onto the train conveyor. In particular, these gating systems are made up of clamshell-type gates that are pivoted about an axis parallel to the train conveyor. These clamshell-type gates assist in controlling the flow of material onto the train conveyor.
After experimentation with the physical embodiment of the concept of U.S. Pat. No. 4,925,356, presently produced under the trademark "DUMP TRAIN", it was found that the clamshell-type gates as used on the DUMP TRAIN were the perfect solution to the passing of bulk commodities from the hopper onto the conveyor belt. Unfortunately, these clamshell-type gates, and the associated hopper structure, were particularly heavy. Under the rules and regulations which affect railroad operations, the amount of cargo that a particular hopper car can carry is limited, in part, by the weight of the hopper car itself. As the weight of the hopper car is reduced, without sacrificing volume, a greater amount of cargo can be carried. As such, it was felt important to reduce the weight of the clamshell-type gates without sacrificing structural integrity, volume, or functionality.
It is an object of the present invention to provide a hopper construction that increases the structural integrity of the hopper.
It is another object of the present invention to provide a hopper construction that allows for clamshell-type gates to be of reduced weight.
It is a further object of the present invention to provide a hopper construction in which the problem of material briding within the hopper is reduced.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.